Hello, just got back from Galapagos over Christmas and did land-based tours myself. Personally would prefer booking tours direct with agencies based on each island to get the best rates. If booking multiple activities with the same tour operator, do try to negotiate for discounts.
These were the companies i went with:
San Cristobal: Galapagos Xcursion (galapagosxcursion@gmail.com / Whatsapp: +593 96 813 1971)
Isabela: Isabela tour centre (isabeladivecenter@hotmail.com / Whatsapp: +593 96 017 6410)
Santa Cruz: Galapagos Blue Sky** (info@galapagosbluesky.com / Whatsapp: +593 99 611 2077)
**Galapagos blue sky charged a premium for North Seymour tours if you book in advance. In case you decide to book this tour, better to book it "last minute" for better rates.